Grinding fixture



Jain. 4, 1949. G. HOHWART ETAL GRINDING FIXTURE 3 Shuts-Sheet 1 Filed Dec.. 29, 1945 INVENTORn e Mai/r4 Janna/7a A Jan. 4, 1949. e. HOHWART ETAL GRINDING FIXTURE Filed Dec. 29, 1945 3 Sheets-Shee t 2 m M w 94 P 2 f a n.

INVENTOR5.

Patented Jan. 4, 1949 GRINDING FIXTURE George Hohwart, betroit, and John Simmons, Washington, Mich., assignors to N. A. Woodworth Company, Detroit, Mich., a corporation of Michigan Application December 29, 1945, Serial No. 638,235

1 12 Claims. The invention relates broadly to grinding machines. More particularly the invention relates to a fixture adapted to be mounted on a conventional grinding machine and to hold a milling cutter adjacent to the grinding wheel and operative to move the cutter so that the wheel grinds an arcu-ate surface uniformly along the side edges of the cutter teeth.

Considerable difllculty has been experienced in grinding uniform arcuate surfaces along the side edges of the teeth on milling cutters. The top and side surfaces of each tooth are tapered rearwardly to provide clearance with the work and,

as a result, the edges to be ground incline lnwardly and downwardly from the front corners of the teeth. This greatly complicates the job of grinding the teeth uniformly. The radii of the respective surfaces must be held to a fine tolerance and must be identical. Moreover, the

centers of the radii must be identically positioned with respect to the axis of the cutter so that'each tooth does its share of work. If the side edges of the teeth are not ground uniformly the faces of the individual teeth assume different shapes when they are cut back during sharpening. When this occurs the teeth do not engage the work with equal pressures and the efliciency of the cutter is greatly reduced.

An important object of the present invention V is to provide a device that will support the cutter during the grinding operation in such manner that uniform grinding of each tooth is assured.

Another object of the invention is to provide a device of the above mentioned character that operates efficiently regardless of the clearance angles on the tooth.

Still another object of the invention is to provide a device of the above mentioned character that, after the initial setting up operation, automatically positions each tooth properly before the grinding wheel without further adjustment.

Yet another object of the invention is to provide a device of the above mentioned character that is simple in construction, efficient in operation and inexpensive to manufacture.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the drawings forming a part of this specification and wherein like numerals are employed to designate like parts throughout the same,

Fig. 1 is a front elevation of a device embodying the invention and showing the manner in which the milling cutter is adjusted during the initial setting up operation,

a the edge will travel.

Fig. 2 is a top plan view thereof and showing the manner in which the cutter is associated with the grinding wheel,

Fig. 3 is a vertical sectional view taken on the line 3-4 of Fig. 1,

Fig. 4 is a fragmentary, transverse sectional view taken on the line 4'| of Fig. 1,

Fig. 5 is a fragmentary, front elevational view showing a modified construction for holding end mill cutters of the type having tapered shanks,

Fig. 6 is a top plan view of the construction shown in Fig. 5, and

Fig. 7 is a longitudinal sectional view taken on the line '|1 of Fig. 6.

Considered in certain of its. broader aspects the fixture embodying the present invention comprises a base which is adapted to be mounted on the table of a conventional grinding machine. Mounted on the base for swinging movement about a horizontal axis is a cradle which carries the milling cutter and holds it adjacent to the grinding wheel. The part of the cradle which carries the cutter is adjustable to position the edges of the cutter teeth predetermined distances from the axis about which the cradle rotates. In order to make these adjustments easily and quickly, a micrometerlike unit comprising a micrometer barrel and a micrometer slide or movable anvil is detachably mounted to pivot about the same axis as the cradle. When the movable anvil is positioned to engage the top surface of the uppermost cutter tooth, it indicates the distance between that surface and the axis; and, when it is moved to engage the side of the tooth, it indicates the distance that surface is from the axis. Consequently, by adjusting the cutter with the micrometer unit in each of the two positions referred to above, the edge to be ground can be selectively positioned with respect to the axis. Manifestly, if the edge is moved past the axis about which the cradle moves, it will also rock about the axis when the cradle is swung through a predetermined arc; and the distance between the axis and the respective tooth surfaces is the radius about which Once the cutter has been properly adjusted, each tooth assumes the same relative position when it is moved in front of the grinding wheel, and, consequently, an identical curvature is ground on each tooth.

From the foregoing, it will be readily apparent that the device is simple in construction but highly eificient in operation. In order to grind the teeth it is merely necessary for the operator to feed the cutter slowly against the grinding wheel while swinging the cradle through 9. limited, predetermined arc. For this purpose, a handle is attached to parts of the cradle and suitable stop means are provided for limiting its movement so that the grinding wheel does not undercut the side or top surfaces of the teeth. After each tooth has been ground, the cutter is indexed to bring the next tooth in front of the grinding wheel and the operation is repeated. The arrangement is such that all of the teeth are ground uniformily and the ground surfaces of the teeth are identically positioned with respect to the axis about which the cutter rotates.

For a more detailed description of the invention, reference is had to the accompanying drawings wherein A designates the support and B designates the cradle.

It will be observed that the support A comprises a base I8 having longitudinally extending slotted tabs I2 and I4 and horizontally spaced vertical standards I6 and I8. At their upper ends the standards I6 and I8 are provided with horizontally aligned bearings 28 and 22, respectively. As suggested, the support A is adapted to be detachably mounted on the table of a conventional grinding machine. This preferably is done by securing the tabs I2 and I4 to the table by suitable clamps provided on the latter.

The cradle B comprises a substantially Y- shaped yoke portion 24 having arms 26 and 28. At their ends the arms 26 and 28 are provided with lateral extensions 38 and 32, which carry outwardy projecting journals 34 and 36 respectively. As best shown in Fig. 2, the extensions 38 and 32 fit snugly between the bearings 28 and 22 and the journals 34 and 36 extend through the bearings and form pivots about which the cradle B swings. In order to permit assembly of the cradle B on the support A, the journals 34 and 36 are made separate from the extensions 38 and 32 and are removably and closely received in central bores in the extensions 38 and 32 and are secured thereon by cross pins 38 and 48. Lubricant is supplied to the journals through oil cups 42 and 44.

By reference to Fig. 3 it will be observed that the extensions 26 and 28 normally extend horizontally from the bearings 28 and 22 and that the yoke portion 24 is normally disposed vertically at one side thereof with the stem 46 received in a recess 48 provided at one edge of the base I8. While the cradle B can be rocked vertically about the journals 34 and 36. it is continuously urged to the above position by a tensioned spring 49. This spring is disposed in an internal recess provided in the bearing 28 and around the journal 34, one end being attached to the bearing and the other end thereof being attached to the journal.

Disposed between arms 26 and 28 is a slide 58, and supporting the slide is an integral shank 52 which extends through a bore 54 in stem 46. Carried by the slide 58 is a transverse bushing 53 which is adapted to support the cutter 68 and its adjuncts. As best shown in Fig. 3, the cutter 68 is removably mounted on a supporting assembly which generally comprises an arbor 55, a bushing 56, and a hand wheel 58. In practice, the cutter 68 is pushed over the arbor 55 and positioned against the head 62 at one end of the latter. It will be observed that the portion of the arbor 55 adjacent to the head 62 is screw threaded and the cutter 60 is held tightly against the head by a washer 64 and a, nut 86. After nut 66 has been tightened, the bushing 66 Is slipped over the arbor 55 and fastened by a nut 68. The entire assembly is then slipped through the bushing 53, and the handwheel 58 is threaded on the projecting end of bushing 56 and locked against rotation by the set screwl8 which threads in the handwheel 58 and acts through the soft metal plug II against the threads on the bushing 56. By reason of the construction described, the handwheel is adjustable to hold a radial flange I2 at the opposite end of the bushing 56 solidly against the adjacent end of bushing 53 whereby to prevent end play of the cutter assembly in the slide 58.

As best shown in Figs. 2 and 3, the handwheel 58 is positioned at the outer side of the yoke where it is readily accessible for manual oper ation and the cutter 68 is positioned vertically at the inner side of yoke 24 with the uppermost of its teeth I4 disposed adjacent to the grinding wheel 76. The axes of journals 34 and 36 are disposed substantially in horizontal alignment with the center of the grinding wheel I6 and the edge 11 of the uppermost cutter tooth 14 is positioned essentially midway between the journals and substantially in alignment with their axes. Thus, the edge 11 is positioned to engage the outermost portion of the grinding wheel 1'6 and,

' unless the edge is positioned-precisely in alignment with the axes of the journals, it will travel in an arcuate path about the axes and relative to the grinding wheel when the cradle B is swung upwardly.

In order to grind an arcuate surface along the edge I! it is necessary to raise its top surface I8 above the extended axes of journals 34 and 36 and to advance its front surface 88 forwardly of the axes, as indicated by the arrows in Fig. 3 and shown by the dot-and-dash lines 82 and 84. When the cutter 68 is positioned in this manner the radial distance between the extended axes and the top and front surfaces 18 and 88 define the radius about which the edge 11 moves and, consequently, the character of the arcuate surface to be formed on the tooth I4.

Vertical adjustment of the edge I1 is obtained by means of a spindle 86. This spindle extends transversely through yoke 24 and carries a fixed pinion 88 which meshes with a rack 98 carried by and extending longitudinally along the slide shank 52. At its outer end the spindle 86 is provided with a socket 92 in which a suitable tool can be inserted and engaged to rotate the pinion 88. Manifestly, the shank 52, and consequently the cutter 68, is raised or lowered depending upon the direction in which the pinion 88 is rotated. The cutter 68 is held solidly in the selected adjusted position by a set-screw 94 and a follower 36. The set-screw is threaded into yoke 24 and presses against a follower 96 which has a curved end sur face 98 positioned to seat solidly against the shank 52. When set-screw 94 is tightened, follower 95 moves into binding engagement with the shank 52 and holds it locked against movement in any direction. On the other hand, when set-screw 94 is loosened, the plug 96 releases shank 52 which can then be adjusted to raise or lower the cutter 68 as hereinabove described.

' Forward adjustment of the edge 11 is obtained in substantially the same manner, as best shown in Fig 1. A spindle I88 extends downwardly into the slide 58 at one side of the bushing 53 and carries a fixed pinion I82 which meshes with a rack I84 carried by and extending longitudinally along the bushing. At its upper end the shaft I88 is similarly provided with a socket I66. By inserting a suitable tool in socket I06 the pinion I62 can be rotated to either advance or retract bushing." and, consequently, the cutter 60. The means for holding bushing 53 in a selected adjusted position is identical to the means described in connection with shank 52. A set screw I08 is threaded into the slide 50 at the opposite side of bushing 63, and it presses against a follower I I which similarly is provided with an arcuate surface II2 positioned to engage the bushing. It will be readily apparent that, when set screw I08 is tightened, the follower I I0 holds bushing 53 stationary, and, when the set screw is loosened, the follower IIO releases bushing 52 for adjustment. Y

The distance edge 1'! is moved relative to the extended axes of journals 34 and 36 is determined by means of a micrometerlike unit which comprises a micrometer barrel and a movable anvil I26. The barrel H4 is carried by a U-shaped bracket II6 which is pivotally supported at one end by a fixed center II8 on the inner end of journal 34 and at its other end by an adjustable center I20 at the inner end of journal 36. Preferably the adjustable center I20 comprises a screw I22 which extends axially through journal 36. At its inner end the screw I22 is pointed to define a pivot for the bracket H6, and at its outer-end the screw is provided with a head I24 by which it can be manually actuated. Centers H8 and I20 fit in suitable sockets provided in the bracket I I 6 and automatically position the end I26 of the movable micrometer anvil I26 in precise alignment with the extended axes of the journals when the micrometer is set at zero.

To mount the micrometer on the device it is merely necessary to retract screw I22 and engage the bracket II6 with the fixed center I I8. When member I22 is screwed inwardly, the pointed end I20thereof engages the bracket H6 and holds it securely but pivotally associated with the cradle frame. Manifestly, since both the centers I I8 and I20 are disposed on the axis about which the cradle frame moves, end I25 of the movable anvil I26 remains on the axis in any position of the bracket II6 as long as the micrometer is adjusted to give a zero reading.

From the foregoing it will be readily apparen that. by using the micrometer assembly, the critier 60 can be selectively positioned so that the grinding wheel 16 cuts an arcuate surface of the desired radius on cutter teeth I4. For example, if it is desired to cut an arc having a radius of .200 inches, the cutter 60 is assembled on .Ithe cradle frame in the manner hereinabove described and the bracket I I 6 is mounted on the centers I0 and I 20. When the bracket I I6 is positioned vertically, as shown in Fig. 1, the movable anvil is positioned to engage the top surface 18 of the uppermost cutter tooth I4. Since the micrometer reads zero when the end I25 of anvil I26 is on the pivotal axis, it can be used to indicate the distance surface I8 is moved past the axis. In practice the cutter 60 is adjusted gradually and periodic readings are taken with the micrometer. These operations are repeated until the cutter 60 is properly positioned with respect to the pivotal axis. According to the present example, the cutter 60 is raised in the manner hereinabove described until the micrometer II4 indicates that top surface 18 is .200 inches above the axes. After the cutter 60 has been positioned vertically, bracket I I6 is swung horizontally so that the movable anvil I26 is positioned to engage the front surface 80 of the cutter tooth. The cutter is then adjusted forwardly in the manner hereinabove described, and it will be readily apparent that the distance the surface 80 is moved past the extended axes of journals 34 and 36 will be indicated by the micrometer. According to the present example, the cutter is moved forwardly until the micrometer indicates an advancement of .200

inches past the axes.

After the cutter 60 has been selectively positioned in the above manner, bracket I I6 is preferably removed and the table of the grinding ma;- chine is adjusted to move the cutter relative to the grinding wheel 16. In the present example, the cutter is advanced until either the top surface II or the front surface of tooth I4 just touches the periphery of the grinding wheel I6, and the usual stops which limit movement of the table are then set to prevent movement past this point. The table is then retracted and the edge to be ground is pressed against the rotating grinding wheel I6 while the cradle B is being swung through a predetermined arc.

Manifestly, in a cutting operation of the type hereinabove referred to, the cradle B must be limited to movement through an arc of otherwise, the grinding wheel 16 will undercut the top and front tooth surfaces I8 and 80. Means for rocking the cradle B and limiting swinging movement thereof is now described in detail.

As best shown in Fig. 1, the journal 34 projects beyond the bearing 20 and carries a disk I28 which is provided adjacent its periphery with an annular series of circumferentially spaced holes I30. At its center, the disc I28 is provided with a hub I32 which seats against the outer end of bearing 20 and is attached to the journal 34 by a pin I33. A hand e I 34 is positioned vertically above'the'hub I32 at the inner side of disc I28. The shank portion I36 of the handle is attached to the disc I28 by a bolt I38. The latter extends through one of the holes I30 and into an internally threaded hole provided in the shank I36, At its lower end the shank I36 is provided with bifur-cations I40 and I42 which embrace the hub I32 and prevent the handle from twisting or pivoting about the bolt I38. Thus, when handle I34 is pushed forwardly, the cradle B swings upwardly about journals 34 and 3'3 against the action of spring 43; and, when the hand'e is released, spring 40 automatically returns the cradle to a vertical position.

Swinging movement of the cradle B is limited by a pair of angularly adjustable, radially extending arms I44 and I46. These arms are mounted on the journal 34 beside disc I28 and held securely in place by a nut I48. Arms I44 and I46 are held in fixed angular relation with each other by locking pins I49 each of which extends through its respective arm and into one of the holes I30. At their distal ends, arms I44 and I46 carry stops I50 and I52, and these stops are positioned to engage a pin I54 which is carried by and projects outwardly from the vertical standard I6. Preferably, each of the stops I50 and I52 comprises a threaded stud I56 which is screwed into a suitable hole provided in its respective arm which stud is held in a selected adjusted position by a lock nut I58. The holes I30 are spaced too far apart to permit fine adjustment of the arms but it will be readily apparent such adjustment ieinbe obtained by suitably positioning the studs In the example given, stops I50 and I52 are positioned 90 apart and stop I52 is normally held against the pin I54 by spring 48. As sug.

by the stops I and I52; and, during these operations the table is advanced until it engages the table limiting stops on the grinding machine.

Cutter is prevented from turning during the grinding operation by means of an indexing arm I60. This arm is adapted to be mounted in either of the openings I62 or I60 provided in arms 26 and 28, respectively. Arm I60 can be manipulated either manually or by means of a suitable tool which is adapted to fit the projecting outer end I65 thereof. At its inner end the'arm I60 is provided with an angular extension I66 which projects into the interstice ahead of the uppermost cutter tooth 14' as best shown in Fig. 2. As

will be apparent, when indexing ar-m I60 is so is. prevented from rosaid journals means for rocking the cradle manu uppermost tooth the indexing arm I60 is pivoted to release the same and the cutter 60 is rotated to bring the next tooth in front of the grinding wheel 16. The indexing arm I60 is then again positioned to hold the cutter 60 against rotation.

When the cutter 60 is carried by the cradle B in the manner shown in the drawing the indexing'arm I60 is-positi oned in opening I62. How'- ever, when the cutter 60 is reversed to grind the opposite edges of teeth 14, the indexing arm I30 will be mounted in the hole I64 in order to en- I gage the end I66 thereof with the cutter teeth.

Figs. 5-7 show a modified fixture assembly for supporting an end mill cutter of the. type having a tapered shankl68. In this form of the invention the slide 50 is provided with a recess I10 which receives .the inner portion of cutter 60, and the outer portion of bushing 53 extends. through and projects from a collar I12 which is attached to the slide by screws I14. Rack I04 is mounted 'on the projecting portion of bearing 53 and the shaft I00 is carried by a bracket" I16 which ne'r with the end of the diamond aligned withthe center of the wheel 16. Thus, by operating 7 the table the tip of the diamond can be moved across the face of the wheel.

It is to be understood that the forms of the invention herewith shown and described are to be taken as preferred examples of the same and that various changes in the size, shape and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the appended claims.

Having thus described the invention, we claim:

1. A grinding fixture for milling cutters com-' prising a support having spaced horizontal bearings disposed in alignment with each other; a cradle frame having journals mounted in said bearings and adapted to rock about said journals; a manually operable handle attached to one of said journals for use in rocking said cradle frame on said journals; adjustable means for limiting rocking movement of the cradle frame; means carried by said cradle frame and disposed at one side of the axis about which it moves adapted to position and hold a cutter with the side and end surfaces of at least one of its teeth predetermined distances from said axis; and pivoted means engageable with the mentioned surfaces of said cutter to limit movement of the latter beyond said predetermined distances.

2. A grinding fixture for milling'cutter com-. prising a support having spaced horizontal bearings-disposed in alignment with each other; a cradle frame having journals mounted for rotation in saidbearings and adapted to rock about ually at a point remote from the cutter; a slide carried by said cradle frame; means for adjustably mounting a cutter on the slide for movement in a direction normal to the axis of said journals; means for adjusting the slide in a direction normal to the direction of said first adjustment, the arrangement being such that the side and end surfaces of at least one of the cutter teeth can be positioned predetermined distances from the journal axis; and a single pivoted means engageable with the mentioned surfaces of said cutter to limit movement of the latter beyond said predetermined distances. I

'3. A grinding fixture for milling cutters comprising a support having spaced horizontal bearings disposed in alignment with each other; a cradle frame having a yoke portion and lateral extensions on the ends of the yoke arms, said extensions provided with journals mounted in the bearings so that said yoke portion can be swung in an arcuate path about a fixed axis; means carried by said yoke portion for holding a cutter between said bearings and with the side and end surfaces of at least one of its teeth predetermined distances from said axis; and a single pivotally operable and radially adjustable means engageable with the mentioned surfaces of said cutter to limit movement of the latter beyond said predetermined distances. I

4. A grinding fixture for milling cutters comprising a support having spaced horizontal bearings disposed in alignment with each other; a'

cradle frame having a yoke portion' and lateral extensions on the ends of the yoke arms, said extensions provided with journals mounted in the bearings so that the yoke portion can be travel of said slide and a single pivotally swingable and radially adjustable means selectively engageable with the side and end surfaces of said cutter teeth, the arrangement being such that by selectively positioning said single pivoted means in confronting relation to the side and end surfacesof the cutter teeth and moving the surfaces against the pivoted means, said surfaces can be positioned predetermined distances beyond said fixed axis. 5. A grinding fixture for milling cutters comprising a-support having spaced'horizontal bearings disposed in alignment with each other; a cradle frame having a yoke portion 'and lateral extensions on the ends of the yoke. arms, said extensions provided with journals mounted in the bearings so that said yoke portion can be swung in an arcuate path about a fixed axis; a slide between the arms of said yoke portion; means for adjusting said slide longitudinally along the arms; a mounting for the cutter carried by said slide; means for adjusting the mounting in a direction at right angles to the direction of travel of said slide; pivotal support means between said journals; and a micrometer carried by said support means and provided with a movable anvil which is adjustable radially to said fixed axis, said movable anvil adapted to engage the side and end surfaces of the cutter teeth and to indicate the position of said surfaces with respect to said fixed axis.

6. A grinding fixture for milling cutters comprising a support having spaced horizontal bearings disposed in alignment with each other; a cradle frame havinga yoke portion and lateral extensions on the ends of the yoke arms, said extensions provided with journals mounted in said bearings so that the yoke portion can be swung in an arcuate path about a fixed axis; a slide between the arms of said yoke portion; means for adjusting said slide longitudinally along the arms; a mounting for the cutter carried by said slide; means for adjusting the mounting in a direction at right angles to the direction of travel of said slide; a radially adjustable gage means engageable with the side and end surfaces of said cutter teeth to position said surfaces properly with respect to said fixed axis; a manual actuator fixed to at least one of said journals for moving said cradle frame about said fixed axis; and an adjustable stop means for limiting swinging movement of the cradle frame.

7. A grinding fixture for milling cutters comprising a support having spaced horizontal bearings disposed in alignment with each other; a cradle frame having a yoke portion and lateral extensions on the ends of the yoke arms,- said extensions provided with journals mounted in the bearings so that the yoke portion can beswung in an arcuate path about a fixed axis; a slide between the arms of said yoke portion; means for adjusting said slide longitudinally along the arms; a mounting for the cutter carried by said slide; means for adjusting the mounting to move the cutter in a direction at right angles to the direction of travel of said slide, the arrangement being such that by selectively adjusting the slide and the mounting the side and end surfaces of at least one of the cutter teeth can be positioned predetermined distances from said fixed axis; pivotal support means between the Journals, and a micrometer carried by said pivotal support means and provided with a movable anvil which is adjustable radially to said fixed axis, said 'movable anvil adapted to engage the side and. end surfaces of the cutter teeth and to indicate the position of said surfaces with respectto said'flxed axis.

8. A grinding fixture for milling cutters comprising a support a cutter holding device pivoted on the support including means for adjusting the cutter in two directions 90 apart and both normal to the pivotal axis; and a pivotally mounted micrometer assembly having an element mounted for adjustment radially of the pivotal axis and engageable with the top and side surfaces of the cutter teeth to indicate the distances between the top and side sinfaces of the cutter teeth and the pivotal axis.

9. A grinding fixture for milling cutters comprising 'a support; a cutter holding device pivoted on the support including means for adjusting the cutter in two directions at right angles to each other and both normal to the pivotal axis; and a micrometer assembly mounted to move about the pivotal axis and having a movable anvil arranged transversely and adjustable radially to the pivotal axis and with its end disposed on said axis when the micrometer is adjusted to give a zero reading, whereby the anvil is adapted to indicate the distances between the top and side surfaces of the cutter teeth and the pivotal axis.

10. A grinding fixture for milling cutters comprising a support; a cutter holding mechanism pivoted on the support including means for adjusting the cutter in two directions at right angles to each other and both normal to the pivotal axis; centers on said pivotal axis; a supporting bracket mounted on said centers; and a micrometer carried by the bracket adapted to indicate the distances between the top and side surfaces of the cutter teeth and the pivotal axis.

11. A grinding fixture for milling cutters comprising a support; a cutter holding mechanism pivoted on the support including means for adjusting the cutter in planes normal to and parallel to the pivotal axis; centers on said pivotal axis, at least one of said centers being adjustable; a supporting bracket mounted on said centers for movement about the pivotal axis; and a micrometer carried by the bracket adapted to indicate the distance between the top surfaces of the cutter teeth and the pivotal axis and also the distance between the side surfaces of the cutter teeth and the pivotal axis.

12. A grinding fixture for milling cutters comprising a support; av cutter holding mechanism pivoted on the support including means for adjusting the cutter in a plane normal to the pivotal axis and a plane parallel to the pivotal axis; centers on said pivotal axis, at least one of said centers being adjustable relative to the other; a supporting bracket mounted on the centers and adapted to swing about said pivotal axis; a micrometer carried by the bracket and having a movable anvil arranged transversely and adjust'able. radially to the pivotal axis and with its end disposed on said axis when the micrometer is adjusted to give a zero reading, whereby the anvil can be used to indicate 'the distances between the top and side surfaces of the cutter teeth and the pivotal axis.

GEORGE HOH'WART. JOHN SIMMONS.

REFERENCES CITED The following references are of record in the file of this-patent:

UNITED STATES PATENTS Number Name Date 856,662 Smith June 11, 1907 1,039,075 Smith Sept. 17, 1912 1,398,187 Guest Nov. 22, 1921 1,879,413 Einstein et a1. Aug. 7, 1928 2,332,510 Franzen Oct. 26; 1943 FOREIGN PATENTS Number Country Date 354,746 Germany June 14, 1922 381,659 Germany Oct. 17, 1922 

